Siemens SINUMERIK 840D Function Manual page 331

Parameterizing the encoder limit frequency (spindles)
The EQN 1325 absolute encoder made by Heidenhain has an incremental track and an
absolute track.
If a spindle is driven at a speed above the encoder limit frequency of the incremental track, the
substantially lower limit frequency of absolute track must be parameterized as the encoder limit
frequency.
MD36300 $MA_ENC_FREQ_LIMIT
Otherwise an incorrect absolute position would be read because the parameterized encoder
limit frequency is not reached when the measuring system is activated. This would cause a
position offset in the actual value system of the machine axis.
Determining the encoder limit frequency
The encoder limit frequency to be parameterized is derived from the smaller of the two following
limit speeds:
● Encoder
The limit speed or encoder limit frequency is listed in the data sheet of the encoder (e.g., limit
speed = 2000 [rpm])
● NC
Due to the NC-internal evaluation process, the maximum limit speed for which error-free
calculation of the absolute value by the NC is possible is 4 encoder revolutions per
interpolator clock cycle.
For an interpolator clock cycle of, for example, 12 ms: Limit speed = 4 / 12 ms = 20,000 rpm
The limiting frequency corresponding to the limiting speed is calculated to be:
MD31020 $MA_ENC_RESOL (encoder pulses per revolution)
MD10050 $MN_SYSCLOCK_CYCLE_TIME (basic system clock cycle)
MD10070 $MN_IPO_SYSCLOCK_TIME_RATIO (factor for the interpolation cycle)
Note
The position control switching speed relevant for spindles is set according to the encoder
limiting frequency of the absolute value encoder of the spindle:
MD35300 $MA_SPIND_POSCTRL_VELO (position control switching speed)
MD36300 $MA_ENC_FREQ_LIMIT (Encoder limit frequency)
Axes and spindles
Function Manual, 06/2019, A5E47437747B AA
10.9 Referencing with absolute encoders
R1: Referencing
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